This document discusses approaches to teaching complex numbers. It describes an axiomatic approach, utilitarian approach, and historical approach. The historical approach builds on prior knowledge of quadratic equations and introduces complex numbers to solve problems like finding the roots of quadratic and cubic equations. The document also covers definitions of complex numbers, addition, subtraction, multiplication, and division of complex numbers. It discusses pedagogical considerations like using multiple representations and building on students' prior knowledge.
2. CONTENTS
Beertino Yeong Hui
Approaches/pedagogy A level syllabus
Diophantus’s problem Pedagogical Consideration
roots of function Multiplication
Cubic Example and Division of
complex numbers
Complex conjugates
Yu Jie
A level syllabus
Pedagogical considerations
Basic definition & John
Argand Diagram A Level syllabus
Addition and Pedagogical considerations
Subtraction of
complex numbers Learning difficulties
Uniqueness of Complex Numbers
3. APPROACHES/PEDAGOGY
Axiomatic Approach
Common in textbooks.
Start by defining complex numbers as numbers of the form a+ib where a, b are real
numbers.
Back to Table of contents Diophantus’s problem
4. APPROACHES/PEDAGOGY
Utilitarian Approach
Briefly describe Complex Numbers lead to the theory of fractals
It allows computer programmers to create realistic clouds and mountains in video
games.
Back to Table of contents Diophantus’s problem
6. APPROACHES/PEDAGOGY
Historical Approach
Why this approach?
Real questions faced by mathematicians.
Build on pre-existing mathematical knowledge,
Quadratic formula
Roots.
Back to Table of contents Diophantus’s problem
7. APPROACHES/PEDAGOGY
So, how does the approach goes?
First, bring about the quadratic problem.
Tapping on prior knowledge
Quadratic formula.
Roots of an equation.
Followed with definition of root.
Then sub value into root to get a cognitive conflict.
Give another example, this time it’s cubic
Tap on prior knowledge again
Completing Square to get to Completing Cube (Cardano’s Method)
Solve to get a weird answer.
Show that weird answer is 4, and get another cognitive conflict.
Back to Table of contents Diophantus’s problem
8. DIOPHANTUS’S PROBLEM
Diophantus' Arithhmetica (C.E 275) A right-angled triangle has area 7
square units and perimeter 12 units. Find the lengths of its sides.
Approaches/Pedagogy Back to Table of contents Root of Function
16. PEDAGOGICAL CONSIDERATIONS
Operations in complex plane is
similar but not exactly the same
as vector geometry (see complex
multiplication and division)
Building on Prior Knowledge
Rules-Based Approach vs
Theoretical Understanding
SyllabusBack to table of contents (Teaching) Basic Definition
17. PEDAGOGICAL CONSIDERATIONS
Multimodal Representation and usage of similarity in
vector geometry for teaching of complex addition and
subtraction
Algebraic proof for uniqueness of complex numbers
and should it be taught specifically
No ordering in complex plane, not appropriate to talk
about
z1 > z2
ordering is appropriate for modulus, since modulus of
complex numbers are real values
SyllabusBack to table of contents (Teaching) Basic Definition
18. BASIC DEFINITONS
First defined by Leonard Euler, a swiss
mathematician, a complex number, denoted
by i, to be i2 = -1
In general, a complex number z can be
written as
where x denotes the real part and y denotes
the imaginary part
Pedagogical considerationsBack to Table of contents Argand Diagram
19. ARGAND DIAGRAM
z=x+yi
Im(z)
x : Real Part
P(x,y) y : Imaginary
y Part
Important aspect,
common student
error is forgetting
Re(z)
0 x that x,y are both
real valued
Basic DefinitionsBack to Table of contents Addition
20. EXTENSION FROM REAL NUMBERS
(ENGAGING PRIOR KNOWLEDGE)
The Real Axis
Im(z)
(x-axis) represents
the real number
z line.
y
|z| In other words the
real numbers just
have the imaginary
θ part to be zero.
Re(z)
0 x
e.g. 1 = 1 + 0 i
Basic DefinitionsBack to Table of contents Addition
21. ADDITION OF COMPLEX NUMBERS
Complex Addition
Addition of 2 complex numbers
z1 = x1 + y1i, z2 = x2 + y2i
z1 + z2 = (x1 + y1i) + (x2 + y2i)
= (x1 + x2) + (y1 + y2) i
Addition of real and imaginary portions and summing the 2
parts up
Geometric Interpretation (vector addition)
Rationale
Multimodal Representation: Argand Diagram
Engaging prior knowledge: Addition for Real Numbers
Argand DiagramBack to Table of contents Subtraction
22. MMR IN ADDITION
Multimodal Representation used: Pictorial
Geometric Interpretation
Vector Addition
Im(z)
z1 z1+z2
z2
Re(z)
0
Argand DiagramBack to Table of contents Subtraction
23. SUBTRACTION OF COMPLEX NUMBERS
Complex Subtraction
Difference of 2 complex numbers
z1 = x1 + y1i, z2 = x2 + y2i
z1 - z2 = (x1 + y1i) - (x2 + y2i)
= (x1 - x2) + (y1 - y2) i
Subtraction of real and imaginary portions and summing the 2
parts up
Geometric Interpretation (vector subtraction)
Rationale
Multimodal Representation: Argand Diagram
Engaging prior knowledge: Subtraction for Real Numbers
AdditionBack to Table of contents Uniqueness
24. MMR IN SUBTRACTION
Multimodal Representation used: Pictorial
Geometric Interpretation
Vector Subtraction
Im(z)
z1-z2 z1
Re(z)
-z2 0
AdditionBack to Table of contents Uniqueness
25. UNIQUENESS OF COMPLEX NUMBERS
If two complex numbers are the same, i.e. z1 = z2, then their real parts
must be equal, and their imaginary parts are equal.
Algebraically, let z1 = x1 + y1i, z2 = x2 + y2 i, if z1 = z2 then we have
x1 = x2 and y1 = y2
Geometrically, from the argand diagram we can see that if two complex
numbers are the same, then they are represented by the same point on
the argand diagram, and immediately we can see that the x and y co-
ordinates of the point must be the same.
Subtraction Back to table of contents
27. PEDAGOGICAL CONSIDERATIONS
Operations in complex plane is similar but not exactly the same as
vector geometry (see complex multiplication and division)
Limitations in relating to Argand diagram (pictorial) for teaching of
complex multiplication and division in Cartesian form
Building on Prior Knowledge
Rules-Based Approach vs Theoretical Understanding
Syllabus Back to table of contents Multiplication
28. PEDAGOGICAL CONSIDERATIONS
Properties…
of complex multiplication assumed
(commutative, associative, distributive over complex addition)
of complex division assumed
(not associative, not commutative)
of complex conjugates
(self-verification exercise)
Notion of identity element, multiplicative inverse
Use of GC
Accuracy of answers
Syllabus Back to table of contents Multiplication
30. MULTIPLICATION OF COMPLEX NUMBERS
Complex multiplication
Scalar Multiplication
z = x + yi, k real number
kz = k(x + yi)
= kx + kyi
Geometric Interpretation (vector scaling)
k ≥ 0 and k < 0
Rationale
Multimodal Representation: Argand Diagram
Engaging prior knowledge: Multiplication for Real Numbers
Pedagogical considerations Back to Table of contents Division
31. MULTIPLICATION OF COMPLEX NUMBERS
i4n = I, i4n+1 = i, i4n+2 = -1, i4n+3 = -I for any integer n
Explore using GC (Limitations)
Extension of algebraic identities from real number system
(z1 + z2 )(z1 – z2 ) = z12 – z22
(x + iy)(x – iy) = x2 – xyi + xyi + y2 = x2 + y2
ALWAYS real
Rationale
Engaging prior knowledge: Multiplication for Real Numbers
Cognitive process: Assimilation
Pedagogical considerations Back to Table of contents Division
33. DIVISION OF COMPLEX NUMBERS
Solve simultaneous equations
(using the four complex number operations)
Finding square root of complex number
Multiplication Back to Table of contents Conjugates
34. COMPLEX CONJUGATES
Let z = x + iy. The complex conjugate of z is given by z* = x – iy.
Conjugate pair: z and z*
Geometrical representation: Reflection about the real axis
Multiplication: (x + iy)(x – iy) = x2 + y2
Division: Realising the denominator
Rationale
Bruner’s CPA
Recalling prior knowledge, Law of recency
DivisionBack to Table of contents Learning Difficulties
35. COMPLEX CONJUGATES
Properties:
Exercise for students (direct verification)
1. Re(z*) = Re(z); Im(z*) = -Im(z) 7. (z1 + z2)* = z1* + z2*
2. |z*| = |z| 8. (z1z2)* = z1*z2*
3. (z*)* = z 9. (z1/z2)* = z1*/z2*,
4. z + z* = 2Re(z); z – z* = 2Im(z) if z2 ≠ 0
5. zz* = |z|2
6. z = z* if and only if z is real
Rationale
Self-directed learning
DivisionBack to Table of contents Learning Difficulties
36. LEARNING DIFFICULTIES
/COMMON MISTAKES
In z = x + yi, x and y are always REAL numbers
Solve equations using z directly or sub z = x + yi
Common mistake: (1 + zi)* = (1 – zi)
Confused with (x + yi)* = (x - yi)
DivisionBack to Table of contents
38. PEDAGOGICAL CONSIDERATION
Start with a simple quadratic equation
Example: x2 + 2x + 2 = 0.
Get students to observe and comment on the roots.
Rationale:
Bruner’s CPA Approach: Concrete
Engaging Prior Knowledge
SyllabusBack to Table of contents Learning Difficulties
39. PEDAGOGICAL CONSIDERATION
Direct attention to discriminant of quadratic equation
What can we say about the discriminant?
Rationale:
Engaging Prior Knowledge:
Linking to O-Level Additional Maths knowledge
Involving students in active learning (Vygotsky’s ZPD)
SyllabusBack to Table of contents Learning Difficulties
40. PEDAGOGICAL CONSIDERATION
Examples on Solving for Complex Roots of Quadratic
Equations
Expose students to different methods:
Quadratic Formula
Completing the Square Method
Rationale:
Making Connections between real case and complex case
Getting students to think actively
SyllabusBack to Table of contents Learning Difficulties
41. PEDAGOGICAL CONSIDERATION
Different version: What if we are given one complex root?
Example:
If one of the roots α of the equation z2 + pz + q = 0 is 3 − 2i,
and p, q ∈ ℝ , find p and q.
Rationale:
Understanding and applying concepts learnt
SyllabusBack to Table of contents Learning Difficulties
42. PEDAGOGICAL CONSIDERATION
Good to
Fundamental Theorem of Algebra
know
Over the set of complex numbers, every polynomial with real
coefficients can be factored into a product of linear factors.
Consequently, every polynomial of degree n with real coefficients
has n roots, subjected to repeated roots.
Rationale:
Making Connections to Prior Knowledge in Real Case
SyllabusBack to Table of contents Learning Difficulties
43. PEDAGOGICAL CONSIDERATION
Good to
Visualizing Complex Roots
know
Exploration with GeoGebra
Rationale:
Stretch higher ability students to think further
Motivates interest in topic of complex numbers
SyllabusBack to Table of contents Learning Difficulties
44. PEDAGOGICAL CONSIDERATION
Extending from quadratic equations to cubic equations
Can we generalize to any polynomial?
Recall: finding conjugate roots of polynomials with real
coefficients
Rationale:
Making sense through comparing and contrasting
SyllabusBack to Table of contents Learning Difficulties
45. LEARNING DIFFICULTIES
/COMMON MISTAKES
X: complex roots will always appear in conjugate pairs
‘No roots’ versus ‘No real roots’
Difficulty in applying factor theorem
Careless when performing long division
Application of ‘uniqueness of complex numbers’ does
not occur naturally
Pedagogical ConsiderationsBack to Table of contents